The field of the present invention relates to static hydraulic pressure type continuously variable transmissions, and more particularly to such transmissions in which a hydraulic closed circuit is formed between a swashplate type hydraulic pump and a swashplate type hydraulic motor.
A static hydraulic pressure type continuously variable transmission of the type herein referred to is disclosed, for example, in Japanese Patent Application Laid-Open No. 70,968/82 Specification and Japanese Patent Publication No. 38,467/84 Specification.
In conventional static hydraulic pressure type continuously variable transmissions a motor cylinder and a motor swashplate of a hydraulic motor are independently supported on a casing. This can result in a great thrust load, applied to the motor swashplate from a group of motor plungers in sliding contact with the motor cylinder, being borne by the casing during operation. Accordingly, such as casing is preferably to be formed with highly rigid wall thickness, which can be heavy.
In addition, a pump cylinder of such as hydraulic pump and a motor cylinder of such a hydraulic motor are concentrically arranged with the former disposed internally of the latter. In such an arrangement the external large-diameter motor cylinder is heavy.
Furthermore, in a conventional static hydraulic pressure type continuously variable transmission, a pump cylinder of the hydraulic pump is pressed in sliding contact against a distribution board fixedly mounted on the motor cylinder of the hydraulic motor so that working fluids of the hydraulic pump and hydraulic motor are transferred through an oil path extending through the rotary sliding surfaces. Because of this, pressurized oil tends to leak from between the opposed rotary sliding surfaces of the distribution board and the pump cylinder, leading to deterioration of transmission efficiency due to such leakage.
In addition, in a conventional apparatus provided with a variable capacity swashplate type hydraulic motor, a hydraulic servo is connected to a motor swashplate to lightly adjust an angle of inclination of the motor swashplate, as is well known. However, the hydraulic servo-motor has a complicated construction and is expensive.
Moreover, in a conventional construction, a clutch valve and its operating system, which control communication and between the discharge and intake sides of the hydraulic pump for regulating power transmission from the hydraulic pump to the hydraulic motor, project axially from the end of the hydraulic motor increasing the overall length of the transmission. This is particularly true where the hydraulic pump and the hydraulic motor are disposed on one and the same axis.